Method of igniting a gas-discharge lamp

ABSTRACT

The method of igniting a gas-discharge lamp includes the steps of generating an exciting signal T in an operating circuit having an AC voltage generator on receipt of a lamp switch-on signal E by the operating circuit; exciting an ignition resonant circuit connected to a gas-discharge lamp with the exciting signal T to produce a decaying oscillating process, advantageously a decaying oscillating voltage, in the ignition resonant circuit; determining a resonant frequency of the ignition resonant circuit from the decaying oscillating voltage or process with a signal processing circuit, advantageously a microprocessor, connected to the ignition resonant circuit and operating the AC voltage generator at the determined resonant frequency by controlling the AC voltage generator with the signal processing circuit. The apparatus can be shut off or a warning signal generated when a predetermined parameter of the decaying oscillating process is exceeded.

BACKGROUND OF THE INVENTION

The invention relates to an apparatus and a method of igniting agas-discharge lamp. Patent Application P 38 37 422.6-33 discloses amethod of igniting a gas-discharge lamp, in which a voltage surge in aresonant circuit assigned to the gas-discharge lamp is used for thepurpose of lamp ignition. The frequency of the output voltage of aoperating circuit means for operating the gas-discharge lamp is fixedafter switching on at a starting value which generally does notcorrespond to the resonant frequency of the resonant circuit. Thefrequency is subsequently varied in the direction of the expectedresonant frequency. The known adaptive ignition frequency determinationrequires a certain time until the ignition frequency or the resonantfrequency is found.

The book "Identifikation dynamischer Systeme" ("Identification ofDynamic Systems"), Rolf Isermann, Vol. 1, Springer-Verlag 1988, pages23-27 describes different identification methods of processes to becontrolled which use the application of test signals to the process tobe investigated. Pulse signals or stepfunction signals, for example, areused as test signals. The identification of the process to be controlledis carried out at the start of the technical control task, in order tobe able to set controller parameters suitably.

SUMMARY OF THE INVENTION

It is the object of the invention to ignite as quickly as possible agas-discharge lamp to which an ignition resonant circuit is connected. Afurther object is to enhance the operational safety.

The method of the invention finds application in an inventivegas-discharge lamp apparatus including a gas-discharge lamp, an ignitionresonant circuit connected to the gas-discharge lamp, an operatingcircuit means for the gas-discharge lamp connected to the ignitionresonant circuit, the operating circuit means including an AC voltagegenerator connected to the ignition resonant circuit for operating theignition resonant circuit, and a signal processing circuit meansconnected to the ignition resonant circuit for determining a resonantfrequency of the ignition resonant circuit and also connected to the ACvoltage generator for setting the AC voltage generator to oscillate atthe resonant frequency.

According to the invention, the method of igniting a gas-discharge lampcomprises the steps of:

a. generating an exciting signal T in the operating circuit means onreceipt of a lamp switch-on signal E by the operating circuit means;

b. exciting the ignition resonant circuit with the exciting signal T toproduce a decaying oscillating process in the ignition resonant circuit;

c. providing a signal processing circuit means connected to the ignitionresonant circuit for determining a resonant frequency of the ignitionresonant circuit and also connected to the AC voltage generator;

d. determining a resonant frequency of the ignition resonant circuitfrom the decaying oscillating process with the signal processing circuitmeans; and

e. operating the AC voltage generator at the resonant frequencydetermined in step d) by controlling the AC voltage generator with thesignal processing circuit means.

In a preferred embodiment of the invention a signal is generated onovershooting at least one predetermined parameter of the decayingoscillating voltage. This signal can be used to shut off the operatingcircuit means or trigger a warning message.

The method according to the invention has the advantage that a shorttime after the occurrence of a lamp switch-on signal, the ignitionresonant circuit, which is assigned to the gas-discharge lamp forgenerating an ignition voltage, is immediately operated at its resonantfrequency by the circuit means for operating the gas-discharge lamp.Component tolerances and drift with ageing exert no more than a minorinfluence on the ignition process of the gas-discharge lamp.

In a particularly advantageous embodiment, the signal-processing circuitmeans, which detects the decay process of the oscillations of theignition resonant circuit excited by the exciting signal, transmits asignal upon overshooting of at least one prescribable value of a decaycoefficient. This embodiment enables a self-diagnosis of the entirearrangement around the gas-discharge lamp, and, if appropriate, switchesoff the operating circuit means for operating the lamp. Furthermore,enhancing the operational safety is possible by this development, since,for example, touching the lamp connections which conduct high voltage bymaintenance staff can likewise be determined from the decay process, andit is possible to issue an appropriate warning message and, ifnecessary, switch off the operating circuit means.

The method according to the invention is explained in more detail withreference to the following description.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram of an arrangement for igniting a gas-dischargelamp, and FIG. 2 is a graphical illustration showing signalcharacteristics of an input signal, an exciting signal and a voltageoccurring in a resonant circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a gas-discharge lamp 10 to which there is assigned anignition resonant circuit which contains an inductive element 11, acapacitive element 12 and a parasitic loss element 13. The resonantcircuit 11, 12, 13 and the lamp 10 are supplied with energy, which ismade available by an energy source 15, by an operating circuit means 14for operating the lamp 10. The operating circuit means 14 contains an ACvoltage generator 16 for exciting the resonant circuit 11, 12, 13. Alamp switch-on signal E is passed to the circuit means 14 to switch onthe lamp 10. The signals occurring due to an exciting signal T in theresonant circuit 11, 12, 13 assigned to the lamp 10 are detected by asignal-processing circuit means 17 which feeds a control signal 18 tothe operating circuit means 14 and, furthermore, transmits a faultsignal 19. The signal-processing circuit means 17 in FIG. 1 detects, forexample, the voltage U in the lamp 10.

The upper part of FIG. 2 shows the temporal characteristic of the lampswitch-on signal E, with which the operating circuit means 14 is to beactivated to operate the gas-discharge lamp 10. The central part of FIG.2 shows an exciting signal T transmitted by the operating circuit means14 to the ignition resonant circuit 11, 12, 13, and the lower part ofFIG. 2 shows a decaying oscillating voltage U in the resonant circuit11, 12, 13, which is detected by the signal-processing circuit means 17and triggered by the exciting signal T. The envelope of the decayingoscillation is designated by the reference numeral 20.

The mode of operation of the arrangement shown in FIG. 1 is explained inmore detail with reference to the signal characteristics shown in FIG.2.

The switching on of the gas-discharge lamp 10 is triggered by the lampswitch-on signal E, which is fed to the operating circuit means 14.Thereupon, the operating circuit means 14 transmits an exciting signal Tto the ignition resonant circuit 11, 12, 13. The exciting signal T can,for example, be generated by the AC voltage generator 16, which iscontained in the operating circuit means 14. The resonant circuit 11,12, 13 assigned to the lamp 10 is drawn as a series resonant circuit. Itis possible to use further resonant circuit arrangements which lead to avoltage increase in the lamp 10 when they are excited with a specificfrequency. The lamp 10, which is not yet ignited at this point in time,initially has no effect on the electrical behaviour of the arrangementshown in FIG. 1. The exciting signal T excites the resonant circuit 11,12, 13 to oscillations whose voltage U is measured across capacitiveelement 12 by the signal-processing circuit means 17. Instead of voltagemeasurement, measurement of the current in the resonant circuit 11, 12,13 is also possible.

The circuit means 17 determines from the signal characteristic U of theoscillation of the resonant circuit 11, 12, 13 the resonant frequency.For the purpose of the ignition process of the lamp 10, which nowfollows, the circuit means 17 controls the AC voltage generator 16 ofthe operating circuit means 14 via the control signal 18 in such a waythat the AC voltage generator 16 oscillates at the resonant frequencyjust determined. After a short test phase, which serves to determine theresonant frequency of the resonant circuit 11, 12, 13, it is immediatelypossible to excite the ignition resonant circuit 11, 12, 13 at itsactual resonant frequency, and this leads to rapid ignition of the lamp.The determination of the actual resonant frequency has the advantagethat manufacturing tolerances of the elements 11, 12, 13 and of thefurther components, which are not shown in FIG. 1, do not, in common ineach case with their long-term drift, play any role in the ignition ofthe lamp 10.

It is provided according to another embodiment of the method accordingto the invention that the signal-processing circuit means 17 analysesthe decay process of the signal characteristic U. The circuit means 17determines, for example, the envelope 20 of the voltage signal U. Thedecay process arises owing to the parasitic element 13 of the resonantcircuit 11, 12, 13, which in the practical embodiment of the resonantcircuit 11, 12, 13 is generally not provided as a discrete resistor, butis assigned to the inductive element 11 and/or the capacitive element 12as a parasitic loss element, and effects a corresponding damping of theresonant circuit. From the envelope 20, it is possible to determine, forexample, the decay constant or another decay coefficient, with which itis initially possible to conduct self-diagnosis of the entire lamparrangement. The prescription of one or move values of the decaycoefficient permits the detection of excessively strong damping, whichcan indicate an instance of failure. Defects can be detected in theresonant circuit 11, 12, 13, as can short-circuiting or single-sidedearth shorts of the lamp leads. Should a fault occur, the circuit means17 can immediately switch off the operating circuit means 14 via thecontrol signal 18. A fault signal 19 is transmitted, if required.

In a particularly advantageous fashion, the detection of the decayprocesses also enhances the operational safety of the installation,since touching a voltage-conducting part in the lamp circuit bymaintenance staff can likewise be detected from an additional damping ofthe resonant circuit 11, 12, 13, and thereupon the operating circuitmeans 14 can be switched off immediately. The enhancement of operationalsafety plays an essential role in particular when the gas-discharge lamp10 is provided as a lamp in a motor vehicle headlight, and maintenanceor repairs are undertaken on the lamp circuit by persons who at the timedo not suspect that high voltages dangerous to life and limb occur atthis point in the motor vehicle.

The operating circuit means 14 and the signal-processing circuit means17 are largely implemented by software in a microprocessing system.

Elements 14 and 17 may be combined in a single unit or microprocessor.

While the invention has been illustrated and described as embodied in anapparatus and method of igniting a gas-discharge lamp, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed is new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:
 1. Method of igniting a gas-discharge lamp, said gas-dischargelamp being connected to an ignition resonant circuit for generating anignition voltage and an operating circuit means for the gas-dischargelamp, said operating circuit means including an AC voltage generatorconnected to the ignition resonant circuit for operating the ignitionresonant circuit, said method comprising the steps of:a. generating anexciting signal T in the operating circuit means on receipt of a lampswitch-on signal E by the operating circuit means; b. exciting theignition resonant circuit with the exciting signal T to produce adecaying oscillating process in the ignition resonant circuit; c.providing a signal processing circuit means connected to the ignitionresonant circuit for determining a resonant frequency of the ignitionresonant circuit and also connected to the AC voltage generator; d.determining a resonant frequency of the ignition resonant circuit fromthe decaying oscillating process with the signal processing circuitmeans connected to the ignition resonant circuit; and e. operating theAC voltage generator at the resonant frequency determined in step d) bycontrolling the AC voltage generator with the signal processing circuitmeans.
 2. Method according to claim 1, further comprising determiningthe resonant frequency from a decaying oscillating voltage of thedecaying oscillating process.
 3. Method according to claim 2, furthercomprising generating a signal on overshooting at least onepredetermined parameter of the decaying oscillating voltage.
 4. Methodaccording to claim 3, further comprising triggering a warning messagegenerating means with said signal.
 5. Method according to claim 3,further comprising switching off the operating circuit means on receiptof said signal by said operating circuit means.
 6. Gas-discharge lampapparatus including a gas-discharge lamp, an ignition resonant circuitfor generating an ignition voltage connected to said gas-discharge lamp,an operating circuit means for the gas-discharge lamp connected to theignition resonant circuit, said operating circuit means including an ACvoltage generator connected to the ignition resonant circuit foroperating the ignition resonant circuit, and a signal processing circuitmeans connected to the ignition resonant circuit for determining aresonant frequency of the ignition resonant circuit and also connectedto the AC voltage generator for setting the AC voltage generator toproduce an alternating signal at the resonant frequency.